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energysmartdetails from greenbuildingadvisor.com by martin holladay Attic-ventilation strategies e xcept in some specific cases, building codes and shingle warranties require new roofs to be vented. If you’re building a house with an unconditioned vented attic, the necessary attic-ventilation details are fairly straightforward, especially if the house has a gable roof. They include soffit vents (and usually a ridge vent) along with ventilation baffles that provide open pathways for air to travel from the soffit vents along the underside of the roof sheathing to the ridge. Although the essential components for attic ventilation are straightforward, mistakes are common. Believe it or not, sometimes it’s as simple as the fact that the roofers forgot to cut back the roof sheathing at the ridge before they installed the ridge vent. Here are some key points to remember. Provide enough clearance between top plates and roof sheathing If you plan to install 14 in. of insulation on your attic floor, then you should have at least 16 in. of clearance between the top plate of your perimeter walls and the underside of your roof sheathing. To make sure that your clearance is adequate, order raised-heel trusses. For a stick-framed roof, set your rafters on a raised 2x plate installed on top of your attic floor joists. don’t use flimsy or undersize ventilation baffles Some energy experts believe that the codeminimum ventilation-gap height (1 in.) is inadequate. Even if you’re willing to accept a 1-in. airspace, many commercial ventilation baffles are so flimsy that they easily collapse when insulation is blown or tucked into place, which can leave an airspace that measures 1⁄2 in. or less. Joseph Lstiburek, a principal at Building Science Corporation, 86 FINE HOMEBUILDING anatomy of a vented roof A vented roof uses open spaces in the soffit and ridge to channel airflow beneath the roof sheathing via baffles located between the rafters. Raised plate provides adequate clearance for insulation. Ventilation baffle 1-in. minimum space between roof sheathing and baffle Soffit vent Rigid insulation installed in rafter bays over the top plate prevents wind washing. Drawing: Steve Baczek, Architect